diff --git a/packages/bezier-react/src/utils/assertUtils.ts b/packages/bezier-react/src/utils/assertUtils.ts
index e3ab109250..686d5493b2 100644
--- a/packages/bezier-react/src/utils/assertUtils.ts
+++ b/packages/bezier-react/src/utils/assertUtils.ts
@@ -1,4 +1,4 @@
-export function isDev() {
+function isDev() {
   return process.env.NODE_ENV !== 'production'
 }